Each year, ocean-faring vessels from overseas discharge enough of this ballast water in US waters to fill about 20,000 Olympic-sized swimming pools, reports Bina Venkataraman for Boston.com.
According to the news organisation, with the discharged ballast water come tiny hitchhikers from afar - invasive species of algae, invertebrates, and young crabs and fish picked up in distant harbors.
These invaders - which threaten to crowd out the sea life native to our waters, and can even pose dangers to humans - are arriving in greater numbers, aided by the rise of global trade, and the advent of faster ships. At the same time, climate change is expected to allow some of these invasive species to thrive farther north than in the past.
All this has sent engineers, scientists, and coastal resource managers scrambling to find ways to deal with these marine invaders before it's too late.
The Threat of Ships
US - Crisscrossing the seas on global trade routes, cargo ships suck up billions of tonnes of water to provide a steadying weight, and then dump that water back into the ocean when it's time to take on new cargo.
